Actuator

ABSTRACT

An actuator is constructed so that the rotor is rotated within the range of a preset angle in a direction corresponding to the direction of current supply to the stator coil. The rotor includes a column-shaped permanent magnet having surfaces perpendicular to a center line of rotation and a surface surrounding the center line of rotation and a frame body configured integrally with the permanent magnet. The frame body covers two center portions of rotation of the permanent magnet and the surface surrounding the center line of rotation of the permanent magnet so that a plurality of exposed surfaces are provided. Each of areas in which these center portions of rotation are covered is provided with a journal supported by the bearing of the stator, and a portion extending in the radial direction from one of the center portions of rotation is provided with the out-put pin to be parallel to the center line of rotation.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a miniature current-controlled actuatorin which when a stator coil is energized, a rotor with a permanentmagnet is rotated through a preset angle in a direction corresponding toa direction in which the stator coil is energized.

[0003] 2. Description of Related Art

[0004] In the technical field of a camera, a miniaturecurrent-controlled actuator, sometimes referred to as a moving-magnetmotor, is known. This actuator is constructed so that when a stator coilis energized, a rotor with a permanent magnet is rotated within therange of a preset angle in a direction corresponding to a direction inwhich the stator coil is energized, and an output pin actuatedintegrally with the permanent magnet drives a member to be driven. Theactuator, in contrast with a stepping motor, has significant advantagesof affording low cost, compactness, and small power consumption. Thus,in the camera, it is chiefly used as a driving source for shutter bladesor stop blades, but its application is not limited to the camera and canbe made to various products.

[0005] For such actuators, various structures have been proposed andused, and typical examples of the structures in recent years are setforth in Japanese Patent Kokai Nos. 2000-197326 and 2000-292827. Theactuators described in these publications are such that although thestructures of stators, as well as those of rotors, are different fromeach other, magnetic poles magnetized in the radial direction ofindividual permanent magnets are equal in number, and even though therotors are replaced with each other, they will function properly,insofar as they gives rise to no shape or dimension problems. Although,for the rotor, one described in the former publication appears to besimpler in fabrication, it entails the high cost of material and is hardto obtain a great magnetic force (high magnetic flux density).Consequently, in most cases, one described in the latter publication isused as an actuator for cameras.

[0006] Here, the structure of the rotor of this type will bespecifically explained. The permanent magnet magnetized in the radialdirection has a cylindrical shape. A rotary shaft which lies in a hollowportion of the permanent magnet and whose ends projecting therefrom aresupported by bearings of the stator and an output pin (driving pin)located in the radial direction are integrally constructed of syntheticresin. Such an output pin is often provided as a single one. Even withthe use of the actuator in the camera, however, two output pins may beprovided at symmetrical positions of 180°, depending on the structure ofthe shutter blades or the stop blades, and the number of pins can bechosen properly in accordance with a desired specification. Such acomponent part made of synthetic resin, after being fabricated as anindependent member, may be attached to the permanent magnet bycementation or force fit. In view of cost, however, it is advantageousto attach the component part to the permanent magnet on molding thecomponent part through a so-called outsert process of injection molding.

[0007] For this actuator also, the need for further compactness hasrecently been emphasized. However, in the actuator of the type set forthin the above Kokai No. 2000-292827, the outside diameter of acylindrical stator has already been reduced to as small as 4-5 mm, andthe permanent magnet of the rotor has also been reduced to as small as 2mm in diameter. Thus, the situation is that further compactness isextremely difficult. In particular, in the permanent magnet of therotor, even when such a small diameter is slightly reduced, theproportion of a reduction in mass is increased, and it becomes difficultto ensure a preset magnetic force or to positively obtain permanentmagnets within tolerances for mass production. As such, when an attemptis made to achieve further compactness, the problem arises that cost isgreatly increased.

[0008] It is thus conceivable that the permanent magnet is configuredinto a column shape so that even when the diameter is reduced, masswhich remains unchanged can be ensured. When the permanent magnet isconfigured into a column shape without reducing the diameter, a greatmagnetic force is necessarily obtained. In such a case, however, aquestion arises as to how portions supported by the bearings and theoutput pin are constructed. In order to solve this, the structure thatthe portions supported by the bearings and the output pin are fabricatedas independent parts of special shapes so that the permanent magnet isattached to them by cementation or force fit has been proposed. However,as parts diminish in size, it becomes difficult to set up the parts, oneby one, by cementation or force fit and to positively produce goodrotors, and actuators thus fabricated involve high cost as a matter ofcourse.

SUMMARY OF THE INVENTION

[0009] It is, therefore, an object of the present invention to provide aminiature, low-cost current-controlled actuator in which a stator coilis supplied with a current and thereby a rotor is rotated within therange of a preset angle in a direction corresponding to a direction inwhich the stator coil is supplied with the current, so that the rotor isfabricated integrally with portions supported by bearings and an outputpin with respect to a column-shaped permanent magnet, through asynthetic-resin injection molding process.

[0010] In order to achieve the above object, the actuator of the presentinvention is constructed so that the rotor is rotated within the rangeof a preset angle in a direction corresponding to the direction ofcurrent supply to the stator coil. In this case, the rotor includes acolumn-shaped permanent magnet having surfaces perpendicular to a centerline of rotation and a surface surrounding the center line of rotationand a frame body configured integrally with the permanent magnet. Theframe body covers two center portions of rotation of the permanentmagnet and the surface surrounding the center line of rotation of thepermanent magnet so that a plurality of exposed surfaces are provided.Each of areas in which these center portions of rotation are covered isprovided with a journal supported by the bearing of the stator, and aportion extending in the radial direction from one of the centerportions of rotation is provided with the output pin to be parallel tothe center line of rotation.

[0011] In the actuator of the present invention, at a place where eachof the center portions of rotation of the permanent magnet is oppositeto the frame body covering each center portion, a polygonal concavity,on one hand, is provided, and on the other hand, a convexity isconfigured to project into the concavity and occupy it. By doing so, thepermanent magnet is favorably constructed integrally with the framebody.

[0012] Further, in the actuator of the present invention, at a placewhere a surface surrounding the center line of rotation of the permanentmagnet is opposite to the frame body covering the surface, concavities,on one hand, are provided, and on the other hand, convexities areconfigured to project into the concavities and occupy them. By doing so,the permanent magnet is favorably constructed integrally with the framebody.

[0013] Still further, in the actuator of the present invention, thepermanent magnet is magnetized as two magnetic poles in the radialdirection, and at least one of the surfaces perpendicular to the centerline of rotation has a groove configured along the boundary between thetwo magnetic poles. The frame body is partially provided in the groove,and the output pin is situated on an extension line of the boundary.Whereby, not only is the integration of the permanent magnet with theframe body favorably maintained, but also the positioning of the outputpin in the direction of magnetization becomes very easy, in view offabrication.

[0014] In the actuator of the present invention, when the frame body isconstructed so that the output pin and another output pin are located atsymmetrical positions of 180° of the permanent magnet, applicationsdifferent from the case of a single output pin can be found.

[0015] This and other objects as well as the features and advantages ofthe present invention will becomes apparent from the following detaileddescription of the preferred embodiments when taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a plan view showing a case where the shutter of ashutter mechanism, viewed from the object side, is closed in a firstembodiment of the present invention;

[0017]FIG. 2 is a sectional view showing essential parts in FIG. 1;

[0018]FIG. 3A is a sectional view showing a cover frame for a stator ofFIG. 2;

[0019]FIG. 3B is a plan view showing the cover frame of FIG. 3A;

[0020]FIG. 3C is a bottom view showing the cover frame of FIG. 3A;

[0021]FIG. 4A is a front view showing a rotor of FIG. 2;

[0022]FIG. 4B is a plan view showing the rotor of FIG. 4A;

[0023]FIG. 4C is a front view showing a permanent magnet constitutingthe rotor;

[0024]FIG. 4D is a plan view showing the permanent magnet of FIG. 4C;

[0025]FIG. 5 is a plan view showing a case where the shutter of theshutter mechanism, viewed from the object side, is fully opened in thefirst embodiment;

[0026]FIG. 6A is a front view showing a rotor in a second embodiment ofthe present invention;

[0027]FIG. 6B is a plan view showing the rotor of FIG. 6A;

[0028]FIG. 6C is a plan view showing a permanent magnet constituting therotor; and

[0029]FIG. 6D is a center cross sectional view showing the permanentmagnet of FIG. 6C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] In accordance with two embodiments shown in the drawings, thepresent invention will be explained below.

First Embodiment

[0031] This embodiment is such that the actuator of the presentinvention is applied to a shutter mechanism for cameras. The structureof the first embodiment is first explained. In this explanation, it isassumed that the object side is referred to as the surface side, whilethe opposite side is referred to as the back side. In FIG. 1, a shutterbase plate 1, made of synthetic resin, is provided with a circularaperture 1 a and an arcuate slot 1 b, which is shown not in FIG. 1 butin FIG. 5 and whose sectional shape is shown in FIG. 2. To mount anactuator to be described later, the shutter base plate 1 has a pluralityof positioning holes 1 c, only one of which is depicted in FIG. 2. Theshutter base plate 1 is also provided with two hooks 1 d and 1 e, eachhaving flexibility, on the surface side, and three shanks 1 f, 1 g, and1 h for mounting three shutter blades, which will be described later, onthe back side.

[0032] On the back side of the shutter base plate 1, a blade holder 2having the same contour as the shutter base plate 1 is mounted by ameans, not shown, and a blade chamber is interposed between them. Theblade holder 2 is also provided with an aperture 2 a of the same shapeas the aperture 1 a, and the aperture 2 a is placed concentrically withthe aperture 1 a, thereby providing an exposure aperture. The bladeholder 2 has a slot 2 b, only a section of which is shown in FIG. 2, ofalmost the same shape as the slot 1 b at a position opposite to the slot1 b. In addition, the blade holder 2 is provided with three holes,although not labeled in the figure, into which the shanks 1 f, 1 g, and1 h of the shutter base plate 1 are fitted.

[0033] Three shutter blades 3, 4, and 5 are arranged in the shutterchamber. The shutter blade 3 has a circular hole, not labeled in thefigure, and a slot 3 a, and the shank 1 f is fitted into the circularhole so that the shutter blade 3 can be rotated. The shutter blade 4 hasa circular hole, not labeled, and a slot 4 a, and the shank 1 g isfitted into the circular hole so that the shutter blade 4 can berotated. The shutter blade 5 has a circular hole, not labeled, and aslot 5 a, and the shank 1 h is fitted into the circular hole so that theshutter blade 5 can be rotated.

[0034] On the surface side of the shutter base plate 1, the actuator ismounted. The first embodiment is such that a base frame 6 of theactuator is mounted directly to the shutter base plate 1. The base frame6 is made of synthetic resin, and a plurality of pins 6 a (two of whichare shown in FIG. 2) are fitted into the positioning holes 1 c of theshutter base plate 1 so that the base frame 6 is fixed to the shutterbase plate 1 by the two hooks 1 d and 1 e mentioned above. The baseframe 6, as shown in FIG. 2, is provided with a bearing hole 6 b for arotor to be described later, beneath which a concave groove 6 c formounting a coil to be described later is configured. The base frame 6has a projection 6 d, an arcuate slot 6 e, and a hole 6 f as well.

[0035] In FIG. 2, a cover frame 7 made of synthetic resin is placedabove the base frame 6. FIGS. 3A-3C show the cover frame 7 itself Thiscover frame 7 is such that an upper plate in FIG. 3A, as seen from FIG.3B, assumes a disk-like shape as a whole and is provided with a bearinghole 7 a for a rotor described later at about the middle thereof. Inorder to mount a coil described later, three U-shaped concave grooves 7b, 7 c, and 7 d are configured, including a surface provided with thehole 7 a.

[0036] A lower plate in FIG. 3A is divided into two segments: oneconnected to the upper plate through two columns 7 e and 7 f, and theother connected to the upper plate through two columns 7 g and 7 h. Oneof the two segments has a step 7 i and the other has a pin 7 j. The step7 i is engaged with the projection 6 d of the base frame 6, therebyserving to prevent the rotation of the pin 7 j fitted into the hole 6 fof the base frame 6. In this way, the cover frame 7 has four elongatedopenings in regard of the four columns 7 e, 7 f, 7 g, and 7 h, and alower opening configured so as to join these openings is partiallyconnected to the slot 6 e of the base frame 6.

[0037] In a space enclosed with the base frame 6 and the cover frame 7,a rotor is placed. The rotor in the first embodiment, as shown in FIGS.4A and 4B, includes a column-shaped permanent magnet 8 and a frame body9 molded integrally with the permanent magnet 8 through an injectionmolding process. As seen from FIGS. 4C and 4D, the permanent magnet 8 inthe present invention is shaped into a column-like form and is notprovided with a hollow such as that of a conventional permanent magnet.Moreover, a column body having two surfaces perpendicular to the centerline of rotation is configured so that four corners of the column bodyof square cross section are rounded off.

[0038] The frame body 9, on the other hand, covers the upper and lowercenter portions of rotation of the permanent magnet 8 and a surfacesurrounding the center line of rotation so that four exposed surfacesare obtained. Individual areas in which these center portions ofrotation are covered have a journal 9 a fitted to be rotatable into thehole 7 a of the cover frame 7 and supported by the hole 7 a as abearing, and a journal 9 b fitted to be rotatable into the hole 6 b ofthe base frame 6 and supported by the hole 6 b as a bearing. Also,although in the first embodiment the journals 9 a and 9 b are providedto the frame body 9 on the rotor side and the holes 7 a and 6 b areprovided to the cover frame 7 and the base frame 6, respectively, on thestator side, the frame body 9 may have two holes so that two journalsfitted into these holes are provided on the stator side, or the hole andthe journal may be provided on each side.

[0039] The frame body 9 has four strips 9 c, 9 d, 9 e, and 9 f and isconfigured so that the cross section of each of the strips 9 d and 9 fis larger in thickness than that of each of the strips 9 c and 9 e.Hence, the strip 9 d is interposed between the columns 7 g and 7 h,while the strip 9 f is interposed between the columns 7 e and 7 f. InFIG. 4B, the permanent magnet 8 is magnetized as two magnetic poles inthe radial direction, with a segment connecting these strips 9 d and 9 fas a boundary. Furthermore, the frame body 9 has a portion extending inthe radial direction and obliquely downward and inserted in the slot 6 eof the base frame 6, and at its top, an output pin 9 g is configuredparallel to the center line of rotation of the permanent magnet 8. Theoutput pin 9 g is inserted in the slot 1 b of the shutter base plate 1and the slot 2 b of the blade holder 2 and is fitted into the slots 3 a,4 a, and 5 a of the shutter blades 3, 4, and 5 in the blade chamber.

[0040] As mentioned above, the rotor is supported to be rotatable to astator frame constructed with the base frame 6 and the cover frame 7,and then a coil 10 is placed in the concave grooves 6 c, 7 b, 7 c, and 7d in such a way that the two bearing holes 6 b and 7 a are covered. Theperipheral surface of the cover frame 7 is fitted into a cylindricalyoke 11 in such a way that the coil 10 is enclosed. Also, the actuatoris constructed so that a magnetic member, which is well known and thusis not shown in the figure, is placed close to the rotor, and thestopped state of the rotor can be maintained by utilizing an attractiveforce exerted between the magnetic member and the permanent magnet 8,even though the coil 10 is not energized.

[0041] Subsequently, the operation of the first embodiment will bebriefly explained. In FIG. 1 showing a closed state of the shutter, theaperture 1 a is closed by the three shutter blades 3, 4, and 5. In thiscase, the coil 10 of the actuator is not energized. In general,therefore, a stopped state of the rotor is very unstable, and there isthe possibility that, for example, when a camera is shaken, the shutterblades 3, 4, and 5 are actuated to expose a film. In the firstembodiment, however, the magnetic member, not shown, is placed close tothe rotor, and thus the rotor is biased to rotate in a counterclockwisedirection by a magnetic force exerted between the magnetic member andthe permanent magnet 8. Since, however, the output pin 9 g comes incontact with the end of the arcuate slot 1 b provided to the shutterbase plate 1, the rotation of the rotor is prevented and this state ismaintained.

[0042] In FIG. 1 of such a state, when the power switch of the camera isturned on, a photometric circuit and a distance-measuring circuit areactuated. Subsequently, when a release button is pressed forphotographing, an electric current is supplied in a forward direction ofthe coil 10. As a result, the rotor is rotated clockwise in FIG. 1, andthe shutter blades 3, 4, and 5 are rotated by the output pin 9 g. Inthis case, the shutter blades 3 and 4 are rotated counterclockwise, withthe shanks 1 f and 1 g, respectively, as centers, and the shutter blade5 is rotated clockwise, with the shank 1 h as a center. Since theshutter blades 3 and 4 are different in the positional relationshipbetween a supporting point and a working point, the rotation of theshutter blade 4 becomes faster than that of the shutter blade 3.Consequently, the amount of superposition of the shutter blades 3 and 4is increased. Such rotation is stopped when the output pin 9 g abuts onthe end of the arcuate slot 1 b provided to the shutter base plate 1,immediately after the opening 1 a is fully opened. This state is shownin FIG. 5, in which the geometry of the actuator is partially omitted.

[0043] Even in a state of FIG. 5, when the exposure time is short, powerto the coil 10 is not disconnected, and when an aperture-closing signalis emitted, a forward current is interrupted and a reverse current issupplied. However, when the exposure time is long, power to the coil 10is disconnected into a non-conducting condition in order to avoidbattery loss. In the first embodiment, the actuator is thus designed sothat even when the coil is brought into such a non-conducting condition,a state of FIG. 5 is favorably maintained. Specifically, in this state,the rotor is biased to rotate clockwise by the magnetic force betweenthe magnetic member, not shown, and the permanent magnet 8.

[0044] After that, when the aperture-closing signal is emitted, thereverse current is supplied to the coil 10. In doing so, the rotor isrotated counterclockwise in FIG. 5, and the shutter blades 3, 4, and 5are rotated in a direction opposite to that described above, through theoutput pin 9 g, to close the aperture 1 a. Such rotation is stopped whenthe output pin 9 g abuts on the end of the arcuate slot 1 b of theshutter base plate 1, immediately after the opening 1 a is completelyclosed by the shutter blades 3, 4, and 5. Also, immediately after therotation of the rotor is stopped, power to the coil 10 is disconnectedto return to a state of FIG. 1, and this state is maintained until thenext photographing.

[0045] In the first embodiment, as mentioned above, the permanent magnet8 is configured into a column shape and hence is capable of obtaining ahigher magnetic flux density than a conventional, cylindrical permanentmagnet. Even when the permanent magnet 8 is made smaller in size thanthe conventional permanent magnet, the same magnetic flux density as inthe conventional permanent magnet can be obtained. Hence, for example,if the dimension of the permanent magnet in the axial direction is thesame, the dimension in the radial direction can be reduced, and as aresult, the diameter of the yoke 11 in the first embodiment can be madesmaller than in a conventional one. Furthermore, if the dimension of thepermanent magnet in the radial direction is made identical, thedimension in the axial direction can be reduced, and thus the verticaldimension of the actuator in FIG. 2 can be made smaller than in theconventional one.

[0046] In the first embodiment, the frame body 9 is configuredintegrally with the permanent magnet 8 through the injection moldingprocess. Even with this process, however, the interface between thepermanent magnet 8 and the flame body 9 is not brought into a completelyfixed condition. As such, if the strips 9 c and 9 e are not configuredin the frame body 9, there is the fear that the permanent magnet 8 ismoved or dropped from the frame body. The first embodiment, however, isconstructed so that such a fear is not absolutely aroused because thepermanent magnet 8 and the four strips 9 c, 9 d, 9 e, and 9 f areconfigured as mentioned above.

[0047] Also, although the permanent magnet 8 in the first embodiment issuch that each surface perpendicular to the rotary axis, as depicted inFIG. 4D, has a shape similar to a square, it may be octagonal, forinstance. In this case, from the above reason, three strips may beprovided. In the first embodiment, as seen from FIG. 4A, strictlyspeaking, a portion provided with the output pin 9 g at the top extendsin the radial direction of the rotor and obliquely downward at an angleof 45°. The present invention is not limited to such a shape, and theabove portion may be designed to extend horizontally. In short, it isonly essential that the portion extends at least in the radialdirection, no matter whether it extends horizontally or obliquely or howlong it extends. The same holds for the case of the second embodiment tobe described later.

[0048] In the first embodiment, in order to improve the efficiency of awinding space of the coil 10 as a link in the chain of compactness, thecover frame 7 is provided with elongated openings between the columns 7e and 7 g and between the columns 7 f and 7 h. If these openings are notnecessary, the cover frame may be constructed so that they are blockedup. An elongated opening provided between the columns 7 g and 7 h servesfor the purpose of preventing the strip 9 d of the frame body 9 fromcoming contact with the cover frame 7. If there is no design problem,this opening may be blocked up. The same holds for the case of thesecond embodiment to be described blow.

Second Embodiment

[0049] The actuator of this embodiment has the same structure as that ofthe first embodiment with the exception that the structure of the rotoris different. Thus, the explanation of the structure of the stator isomitted, but the description of the stator alone and of the relativerelationship between the stator and the rotor in the first embodiment isalso applied to the case of the second embodiment. With reference toFIGS. 6A-6D, the rotor in the second embodiment will be explained below.

[0050] The rotor in the second embodiment includes a permanent magnet 18having a shape similar to a column and a frame body 19 configuredintegrally with the permanent magnet 18 through the injection moldingprocess. The permanent magnet 18 is provided with linear V grooves 18 aand 18 b passing through the center portions of rotation in its twosurfaces perpendicular to the center line of rotation, and linear Vgrooves 18 c and 18 d extending so as to connect the V grooves 18 a and18 b in its peripheral surface. The permanent magnet 18 has two magneticpoles magnetized in the radial direction, and the V grooves 18 a, 18 b,18 c, and 18 d are provided along the boundary between the two magneticpoles. Rectangular parallelepiped-shaped concavities 18 e and 18 f areprovided in the middle portions of the V grooves 18 a and 18 b,respectively, that is, in the upper and lower center portions ofrotation of the permanent magnet 18.

[0051] The frame body 19, on the other hand, has four strips 19 a, 19 b,19 c, and 19 d, of square shapes, having convexities with which the Vgrooves 18 a, 18 b, 18 c, and 18 d and the concavities 18 e and 18 f arecharged. The two center portions of rotation are provided with shanks 19g and 19 h supported by bearings of a stator frame. As described in thefirst embodiment, however, the center portions of rotation may haveholes, instead of the shanks 19 g and 19 h, so that shanks fitted intothe holes are provided on the stator side. Furthermore, the frame body19 has a portion such that the strip 19 c is extended in the radialdirection and somewhat obliquely downward, and at its top, an output pin19 i is configured. Also, the actuator of the second embodiment isoperated in accordance with the first embodiment, and thus theexplanation of the operation is omitted.

[0052] In the second embodiment also, as mentioned above, the permanentmagnet 18 is configured into a column shape and hence is capable ofobtaining a higher magnetic flux density than the conventional,cylindrical permanent magnet. Hence, even when the permanent magnet 18is made smaller in size than the conventional permanent magnet, the samemagnetic flux density as in the conventional permanent magnet can beobtained. Since in the second embodiment the V grooves 18 a, 18 b, 18 c,and 18 d and the concavities 18 e and 18 f are provided around thepermanent magnet 18 and the convexities of the strips 19 a. 19 b, 19 c,and 19 d project into them, it is avoidable that the relative positionsof the permanent magnet 18 and the frame body 19 are shifted and thepermanent magnet 18 is dropped from the frame body 19.

[0053] Also, in the second embodiment, the V grooves 18 a, 18 b, 18 c,and 18 d and the concavities 18 e and 18 f are provided around thepermanent magnet 18, but even though a part or all of them are providedto the frame body 19, the purpose of the present invention can beachieved. Even when all of the V grooves 18 a, 18 b, 18 c, and 18 d andthe concavities 18 e and 18 f are not provided, the purpose of thepresent invention can be achieved, but when only one of them isprovided, the present invention is not worked out. Each of the V grooves18 a, 18 b, 18 c, and 18 d can be replaced by a single hole or pluralityof holes of various shapes. Although each of the concavities 18 e and 18f has a square shape in FIG. 6C, its shape is not limited to the square.However, it is favorable that the concavities 18 e and 18 f areconfigured to be polygonal so that the permanent magnet 18 is notrotated with respect to the frame body 19.

[0054] The permanent magnet 18 in the second embodiment is such that theV grooves 18 a, 18 b, 18 c, and 18 d are configured on molding and twomagnetic poles are magnetized in a direction perpendicular to the Vgrooves 18 a and 18 b. In the case of the two magnetic poles, it isdesirable that the output pin 19 i, as is well known, is situated on anextension line of the boundary between the magnetic poles. As such, whenthe permanent magnet is constructed as in the second embodiment, thesecond embodiment, in contrast with the first embodiment, has theadvantages that the relative positional relationship between the outputpin and the direction of magnetization is surely obtained on fabricationand the relative positions of the permanent magnet 18 and the frame body19 remain unchanged after fabrication. Where there is no need to givespecial consideration to the above description or manufacturing cost,the permanent magnet may be designed so that the two V grooves 18 c and18 d configured in the peripheral surface of the permanent magnet 18 areprovided not at symmetrical positions of 180° as in the secondembodiment, but at positions of different angles. Three or more Vgrooves can be configured in the peripheral surface, as the case may be.

[0055] Also, although in each of the above embodiments a single outputpin is provided, a plurality of output pins can be provided, dependingon the type of a mechanism to be driven. However, the actuator of thistype is extremely small in size, and therefore, in view of fabrication,it is desirable that two output pins are provided. Where the actuatorwith the two output pins is used in a shutter or stop mechanism forcameras, it is optimum that the two output pins are located atsymmetrical positions of 180°.

[0056] The actuator of the present invention, as mentioned above, issuch that the current is supplied to the stator coil and thereby therotor is rotated over the range of a preset angle in the direction ofcurrent supply. The rotor has the column-shaped permanent magnet, andthe portions of the permanent magnet supported by bearings and theoutput pin are integrally constructed through the synthetic-resininjection molding process. Thus, the entire actuator, not to speak ofthe rotor, can be manufactured in small size and at low cost.

What is claimed is:
 1. An actuator in which a rotor is rotated within arange of a preset angle in a direction corresponding to a direction ofcurrent supply to a stator coil, wherein said rotor includes acolumn-shaped permanent magnet having surfaces perpendicular to a centerline of rotation and a surface surrounding said center line of rotationand a frame body configured integrally with said permanent magnet, saidframe body covering two center portions of rotation of said permanentmagnet and said surface surrounding said center line of rotation of saidpermanent magnet so that a plurality of exposed surfaces are provided,each of areas in which said center portions of rotation are covered isprovided with a journal supported by a bearing of a stator, and aportion extending in a radial direction from one of said center portionsof rotation is provided with an output portion.
 2. An actuator accordingto claim 1, wherein said output portion is parallel to said center lineof rotation.
 3. An actuator according to claim 2, wherein at a placewhere each of said center portions of rotation of said permanent magnetis opposite to said frame body covering each of said center portions, apolygonal concavity, on one hand, is provided, and on the other hand, aconvexity is configured to project into said concavity and occupy saidconcavity.
 4. An actuator according to any one of claims 1-3, wherein ata place where a surface surrounding said center line of rotation of saidpermanent magnet is opposite to said frame body covering said surface,concavities, on one hand, are provided, and on the other hand,convexities are configured to project into said concavities and occupysaid concavities.
 5. An actuator according to claim 4, wherein saidpermanent magnet is magnetized as two magnetic poles in a radialdirection, and at least one of surfaces perpendicular to said centerline of rotation has a groove configured along a boundary between saidtwo magnetic poles, said frame body is partially provided in the groove,and said output pin is situated on an extension line of said boundary.6. An actuator according to claim 5, wherein said frame body isconstructed so that said output pin and another output pin are locatedat symmetrical positions of 180° of said permanent magnet.
 7. A bladedriving device for cameras having an actuator in which a rotor isrotated within a range of a preset angle in a direction corresponding toa direction of current supply to a stator coil, wherein said rotorincludes a column-shaped permanent magnet having surfaces perpendicularto a center line of rotation and a surface surrounding said center lineof rotation and a frame body configured integrally with said permanentmagnet, said frame body covering two center portions of rotation of saidpermanent magnet and said surface surrounding said center line ofrotation of said permanent magnet so that a plurality of exposedsurfaces are provided, each of areas in which said center portions ofrotation are covered is provided with a journal supported by a bearingof a stator, and a portion extending in a radial direction from one ofsaid center portions of rotation is provided with an output pin to beparallel to said center line of rotation.
 8. A blade driving device forcameras according to claim 7, wherein said actuator is used as a drivingsource.
 9. A blade driving device for cameras according to claim 8,wherein said blade driving device for cameras in which said actuator isused as a driving source is a shutter device for cameras.
 10. A bladedriving device for cameras according to claim 9, wherein said bladedriving device for cameras in which said actuator is used as a drivingsource is a stop device for cameras.